Evidence that histidine protonation of receptor-bound anthrax protective antigen is a trigger for pore formation

The protective antigen (PA) component of the anthrax toxin forms pores within the low pH environment of host endosomes, through mechanisms that are poorly understood. It has been proposed that pore formation is dependent on histidine protonation. In previous work, we biosynthetically incorporated 2-fluorohistidine (2-FHis), an isosteric analog of histidine with a significantly reduced pKa (~1), into PA, and showed that the pH-dependent conversion from the soluble prepore to a pore was unchanged. However, we also observed that 2-FHisPA was non-functional in the ability to mediate cytotoxicity of CHO-K1 cells by LFN-DTA, and was defective in translocation through planar lipid bilayers. Here, we show that the defect in cytotoxicity is due to both a defect in translocation and, when bound to the host cellular receptor, an inability to undergo low pH-induced pore formation. Combining X-ray crystallography with hydrogen-deuterium (H-D) exchange mass spectrometry, our studies lead to a model in which hydrogen bonds to the histidine ring are strengthened by receptor binding. The combination of both fluorination and receptor binding is sufficient to block low pH-induced pore formation

Copper-Catalyzed Trifluoromethylation of Unactivated Olefins

Activating the inactive: A copper-catalyzed allylic trifluoromethylation of unactivated terminal olefins proceeds under mild conditions to produce linear allylic trifluoromethylated products with high E/Z selectivity (see scheme). The reaction can be applied to a range of substrates bearing numerous functional groups. Furthermore, the reaction is scalable and amenable to a benchtop setup.National Institutes of Health (U.S.) (GM46059)National Institutes of Health (U.S.) (Postdoctoral Fellowship F32GM093532)National Science Foundation (U.S.) (Grant ACHE-9808061)National Science Foundation (U.S.) (Grant DBI-9729592)National Institutes of Health (U.S.) (Grant 1S10RR13886-01

Synthesis and Characterization of Aqueous Cu2ZnSnS4 Nanoparticles for Antimicrobial Applications

Hospital-acquired infection (HAI) is a major public health issue in the United States and in the world. According to a report in 2007 by the Centers for Disease Control and Prevention (CDC), there were approximately 1.7 million HAI and 99,000 deaths from the infection. The estimated annual medical cost to treat HAI is $28 -$45 billion. In addition, HAI's are increasingly resistant to a broad spectrum of antibiotics due in no small part to overuse of antibiotics. As a result, there is an increasing interest in non-antibiotic antimicrobial alternatives. Nanoparticles (NPs) have been shown to have antimicrobial properties and inorganic NPs have the advantages of being not susceptible to degradation by enzymes. Such antimicrobial activities can also be assisted by light for semiconducting NPs such as quantum dots (QDs) due to their photoconductive properties. However, the drawback of commercial quantum dots is that they contain heavy-metal elements such as cadmium (Cd), which is toxic to human and the environment. Although TiO2 NPs are known to exhibit antimicrobial properties and do not contain toxic elements their antimicrobial activities need ultraviolet (UV) light activation which can be harmful to human. The goal of this study is to develop environmentally friendly synthesis route to fabricate non-cytotoxic Kesterite, Cu2ZnSnS4 (CZTS) QDs in water and investigate their antimicrobial properties both in a suspension and as a coating. CZTS is a semiconducting inorganic compound with a near infrared (NIR) band gap that can absorb the whole spectrum of light including UV, visible, and near infrared (NIR). The advantage of CZTS is that it does not contain toxic elements and its small band gap may allow easy reactive oxygen species (ROS) generation and enhanced antimicrobial activities due to their capability to be activated by visible and NIR light. We have successfully made CZTS NP suspensions in water that exhibited a wurtzite crystalline structure. Furthermore, these CZTS NPs showed photoconductivities in powder compacts and exhibited photovoltaic properties when used as an inorganic dye in dye-sensitized solar cells. CZTS NPs were also shown to inactivate growth of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria with white light activation in suspension. While CZTS NPs killed bacteria they were relatively benign to human fibroblast cells (Bj-5ta). Coating studies show that CZTS coating is effective in preventing bacterial growth in light in <30 min, and possibly shorter. Unlike antibiotic coatings which can degrade in days, the inorganic CZTS coating is hardy and durable. These studies indicated the aqueous CZTS QDs may have antimicrobial applications.Ph.D., Biomedical Engineering -- Drexel University, 201

Discovery and development of organic super-electron-donors

Based on simple ideas of electron-rich alkenes, exemplified by tetrakis(dimethylamino)ethene, TDAE, and on additional driving force associated with aromatization, families of very powerful neutral organic super-electron-donors (SEDs) have been developed. In the ground state, they carry out metal-free reductions of a range of functional groups. Iodoarenes are reduced either to aryl radicals or, with stronger donors, to aryl anions. Reduction to aryl radicals allows the initiation of very efficient transition-metal-free coupling of haloarenes to arenes. The donors also reduce alkyl halides, arenesulfonamides, triflates, and triflamdes, Weinreb amides, and acyloin derivatives. Under photoactivation at 365 nm, they are even more powerful and reductively cleave aryl chlorides. They reduce unactivated benzenes to the corresponding radical anions and display original selectivities in preferentially reducing benzenes over malonates or cyanoacetates. Additionally, they reductively cleave ArC−X, ArX−C (X = N or O) and ArC−C bonds, provided that the two resulting fragments are somewhat stabilized

Comparison of Dynamics of Extracellular Accesses to the β(1) and β(2) Adrenoceptors Binding Sites Uncovers the Potential of Kinetic Basis of Antagonist Selectivity.

From the molecular mechanism of antagonist unbinding in the β(1) and β(2) adrenoceptors investigated by steered molecular dynamics, we attempt to provide further possibilities of ligand subtype and subspecies selectivity. We have simulated unbinding of β(1)-selective Esmolol and β(2)-selective ICI-118551 from both receptors to the extracellular environment and found distinct molecular features of unbinding. By calculating work profiles, we show different preference in antagonist unbinding pathways between the receptors, in particular, perpendicular to the membrane pathway is favourable in the β(1) adrenoceptor, whereas the lateral pathway involving helices 5, 6 and 7 is preferable in the β(2) adrenoceptor. The estimated free energy change of unbinding based on the preferable pathway correlates with the experimental ligand selectivity. We then show that the non-conserved K347 (6.58) appears to facilitate in guiding Esmolol to the extracellular surface via hydrogen bonds in the β(1) adrenoceptor. In contrast, hydrophobic and aromatic interactions dominate in driving ICI-118551 through the easiest pathway in the β(2) adrenoceptor. We show how our study can stimulate design of selective antagonists and discuss other possible molecular reasons of ligand selectivity, involving sequential binding of agonists and glycosylation of the receptor extracellular surface